And, know yourself. I did my first century alone, and did not join groups. Same with my first real climbing century last summer. And, this summer for my hardest ride yet, I will also go alone. I like to do hard efforts alone so that I can really tune into how I feel and not get swept along with anyone else's pace or psychology, and not feel that I need to take care of anyone else, either. Listen to your own intuition about yourself and how you operate best.
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury